Nice. Note that Example 2 can be called as such:

my @r = partition { $_ % 3 } [], 0 .. 12;
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and autovivification will create the sub-refs, though only for those elements that actually get assigned to. It's probably best to go ahead and specify the arrayrefs, but it could be a little cumbersome. It can be made simpler by a little tweak: the 2nd argument can be an arrayref or a number; if a number, partition creates that many sub-array(ref)s.

sub partition (&$@)
{
    my $condition = shift;
    my $receivers_ar = shift;
    ref $receivers_ar or $receivers_ar = [ map [], 1..$receivers_ar ];
    push @{ $receivers_ar->[ &$condition ] }, $_ for @_;
    @$receivers_ar
}

my @r = partition { $_ % 3 } 3, 0 .. 12;
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Also note that the map cannot be replaced with ([]) x $receivers_ar because that will make three copies of the same ref.